The clinical importance of BIV infection is not known. The long-term objective of the proposed investigation is to assess the potential for BIV infection in cattle to become clinically significant. Genetic diversity is a common phenomena among RNA viruses because of the lack of an error- correcting activity of reverse transcriptase. Genetic diversity contributes significantly to viral pathogenesis by altering cell tropism and host range the allowing virus to circumvent immune patrol. The specific aim of this study is to examine the genetic diversity of BIV provirus in naturally infected animals. The objectives of this study are as follows: I) PCR amplify the pol and env genes of BIV provirus from field samples. 2) The products of the PCR reactions will be sequenced. 3) Compare the genetic cmposition of a conserved poli and hypervariable env gene regions from samples obtained from members the same herd and members of an unrelated herd. The results from this study could further establish BIV infection of cattle as a large animal model for HIV infection in human.